1. Technical Field
The present invention relates to reconfigurable optical add/drop multiplexer (ROADM) systems and methods of operation and, in particular, to managing added signals in an ROADM node.
2. Description of the Related Art
A reconfigurable optical add/drop multiplexer (ROADM) node is an important optical network element that permits flexible adding and dropping of signals on any or all wavelength division multiplexing (WDM) channels at the wavelength layer. A multi-degree ROADM node (MD-ROADM), which can correspond to a ROADM node with 3 degrees or higher, is another optical network element that also provides a cross-connection function of WDM signals among different paths. Although conventional ROADM nodes have a certain degree of flexibility for adding and dropping signals on WDM channels, they do not possess sufficient flexibility to adapt to rapidly growing and increasingly dynamic Internet-based traffic. For example, transponders of conventional ROADM nodes typically do not have non-blocking and wavelength transparent access to all dense wavelength division multiplexing (DWDM) network ports. As a result, colorless and directionless (CL&DL) MD-ROADM nodes have been widely studied recently to replace conventional ROADM nodes. In this context, “colorless” can refer to ROADM nodes in which transponders can receive and transmit signals on any wavelength employed by the ROADM node system. In turn, “directionless” can refer to ROADM nodes in which transponders can receive signals originating from any input port and can forward signals to any output port.
Some current, proposed methods for building CL&DL MD-ROADM nodes suggest employing a large scale fiber switch, also referred to as a photonic cross-connect (PXC). For example, with reference to FIG. 1, according to these methods, a large scale fiber switch 102 can be implemented at the core of the ROADM node 100. Alternatively, with reference to FIG. 2, other methods suggest implementing large scale fiber switches 202 and 204 between transponders 206 and the multiplexers 208 in the ROADM node 200.